Derivative Financial Instruments (Schedule Of NYMEX Contracts And Butane Price Swap Purchase Agreements) (Details) bbl in Millions	Mar. 31, 2018 bbl
Economic Hedges [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	4.1
Economic Hedges Futures [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	1.0

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

Name:	invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant